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January 26, 2011

Plastic artificial retina is a hit with nerve cells

Light-sensitive plastic might be key to repairing damaged retinas. Creating neuro-prosthetic devices such as retinal implants is tricky because biological tissue doesn't mix well with electronics. Metals and inorganic semiconductor materials can adversely affect the health or function of nerve cells, says Fabio Benfenati at the Italian Institute of Technology in Milan. And over time the body's natural defences can be incredibly hostile and corrosive to such materials.

The emergence of flexible, organic semiconductor materials now offers an alternative. To test them, Benfenati and colleagues seeded nerve cells onto the surface of a light-sensitive semiconducting polymer similar to those used in some solar cells. The cells grew into extensive networks containing thousands of neurons. "We have proved that the materials are highly biocompatible," says Benfenati.

What's more, the presence of the cells did not interfere with the optical properties of the polymer. The team were able to use the neuron-coated polymer as an electrode in a light-driven electrolytic cell.

Artificial colour vision

When short pulses of light were aimed at specific sections of the polymer, only local neurons fired, suggesting the material has the spatial selectivity needed for artificial retinas, says Benfenati.

"It's very elegant science," says Robert Greenberg, whose company Second Sight is close to receiving clinical approval for its retinal prosthesis. But Greenberg questions whether the electrical currents generated would be sufficient to stimulate nerve cells in the eye.

It's still too early to tell, says Benfenati. But he thinks the new material is worth further study, because of another benefit. It can be tuned to respond only to specific wavelengths of light, raising the prospect of creating artificial colour vision, he says.